1. Field of the Invention
This invention relates generally to a method and an apparatus for radiation computed tomography employing a conical radiation beam, and more particularly to improvements in radiation tomography for photographing a moving part of a subject.
2. Description of the Related Art
Radiation tomography for a living organism such as a human body is known and uses a conical radiation (X-ray) beam emitted from a source of radiation. As an example, an X-ray tomograph that collects projection data over the entire circumference of the heart is disclosed in Japanese Unexamined Patent Publication No. 9(1997)-253079. In the X-ray tomograph, the projection data are recorded in synchronization with heartbeats by an electrocardiograph. Because the obtained projection data are not photographed when the states of the heart are all the same, only data for cases where position of the cardiac vein is considered to be the same are sampled and reconstituted.
In the aforementioned conventional example, all projection data are sampled and then only projection data for cases where the position of the cardiac vein is considered to be the same are sampled, so it will take time to sample data and it will be a waste of time. In addition, the influence of radiation on a living organism becomes greater with the lapse of time.
Furthermore, no problem will occur in photographing a part of a living organism that does not move, but there are cases where in photographing a part (such as a heart) that moves periodically, an object to be photographed moves while being irradiated with radiation. When the motion is small, it does not matter. When the motion is large, however, the outline of the image will become obscured, and consequently, there is a problem that a tomogram and a three-dimensional image of high resolution cannot be obtained.